I usually go full Symfony with my projects until I need to spread it out. But even for interactivity, I first go for htmx and Alpine.js instead of full React or so, where I then need to setup API on backend and frontend.

I think once you're deep into a project, you of course know the features needed and the constraints and you'll be more efficient the next time around.

I think the challenge is to keep working on your old legacy projects.

Plus Symfony is quite flexible on how you want to organize your code. Modular monolith, monolith, DDD, microservices, "junior developer just setting up controllers and entities".